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Träfflista för sökning "WFRF:(Åkerstedt Torbjörn) "

Sökning: WFRF:(Åkerstedt Torbjörn)

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31.
  • Abulaiti, Yiming, et al. (författare)
  • A search for top squarks with R-parity-violating decays to all-hadronic final states with the ATLAS detector in root s=8 TeV proton-proton collisions
  • 2016
  • Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :6
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for the pair production of top squarks, each with R-parity-violating decays into two Standard Model quarks, is performed using 17.4 fb(-1) of root s = 8 TeV proton-proton collision data recorded by the ATLAS experiment at the LITC. Each top squark is assumed to decay to a b- and an 8-quark, leading to four quarks in the final state. Background discrimination is achieved with the use of b-tagging and selections on the mass and substructure of large-radius jets, providing sensitivity to top squark masses as low as 100 GeV. No evidence of an excess beyond the Standard Model background prediction is observed and top squalls decaying to bs are excluded for top squark masses in the range 100 <= m((t) over tilde) <= 315 GeV at 95% confidence level.
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32.
  • Abulaiti, Yiming, et al. (författare)
  • Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at root s=8 TeV with the ATLAS detector
  • 2015
  • Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :10
  • Tidskriftsartikel (refereegranskat)abstract
    • An analysis is presented of events containing jets including at least one b-tagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced fourtop-quark production, pair production of chiral b '-quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b ' quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models.
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33.
  • Abulaiti, Yiming, et al. (författare)
  • Analysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the t-channel at root s=8 TeV with the ATLAS detector
  • 2017
  • Ingår i: Journal of High Energy Physics (JHEP). - : Springer Berlin/Heidelberg. - 1126-6708 .- 1029-8479. ; :12
  • Tidskriftsartikel (refereegranskat)abstract
    • The electroweak production and subsequent decay of single top quarks in the t-channel is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of a triple-differential decay rate in t-channel production is used to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb(-1) of proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised W bosons is measured to be f(1) = 0.30 +/- 0.05. The phase between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b-quarks is measured to be delta = 0.002 pi(+0.016 pi)(+0.017 pi), giving no indication of CP violation. The fractions of longitudinal or transverse W bosons accompanied by right-handed b-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [g(R)/V-L is an element of [-0.12, 0.17] and Im [g(R)/V-L is an element of [-0.07, 0.06]. Constraints are also placed on the ratios vertical bar V-R/V-L vertical bar and vertical bar g(L)/V-L vertical bar. In addition, the polarisation of single top quarks in the t-channel is constrained to be P > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.
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34.
  • Abulaiti, Yiming, et al. (författare)
  • Angular analysis of B-d(0) -> K* mu(+)mu(-) decays in pp collisions at root s=8 TeV with the ATLAS detector
  • 2018
  • Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :10
  • Tidskriftsartikel (refereegranskat)abstract
    • An angular analysis of the decay B-d(0) -> K*mu(+)mu(-) is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb(-1) of integrated luminosity collected during 2012 at centre-of-mass energy of root s = 8TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.
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35.
  • Abulaiti, Yiming, et al. (författare)
  • Centrality, rapidity, and transverse momentum dependence of isolated prompt photon production in lead-lead collisions at root S-NN=2.76 TeV measured with the ATLAS detector
  • 2016
  • Ingår i: Physical Review C. - : American Physical Society. - 2469-9985. ; 93:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Prompt photon production in root S-NN = 2.76-TeV Pb + Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb(-1). Inclusive photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality and transverse momentum in two pseudorapidity intervals, vertical bar eta vertical bar < 1.37 and 1.52 <= vertical bar eta vertical bar < 2.37. The scaled yields in the two pseudorapidity intervals, as well as the ratios of the forward yields to those at midrapidity, are compared to the expectations from next-to-leading-order perturbative QCD (pQCD) calculations. The measured cross sections agree well with the predictions for proton-proton collisions within statistical and systematic uncertainties. Both the yields and the ratios are also compared to two other pQCD calculations, one which uses the isospin content appropriate to colliding lead nuclei and another which includes nuclear modifications to the nucleon parton distribution functions.
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36.
  • Abulaiti, Yiming, et al. (författare)
  • Charged-particle distributions at low transverse momentum in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC
  • 2016
  • Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of distributions of charged particles produced in proton-proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 mu b(-1). The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators.
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37.
  • Abulaiti, Yiming, et al. (författare)
  • Charged-particle distributions in pp interactions at root s=8TeV measured with the ATLAS detector
  • 2016
  • Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:7
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents measurements of distributions of charged particles which are produced in proton-proton collisions at a centre-of-mass energy of root s = 8TeV and recorded by the ATLAS detector at the LHC. A special dataset recorded in 2012 with a small number of interactions per beam crossing (below 0.004) and corresponding to an integrated luminosity of 160 mu b(-1) was used. A minimumbias trigger was utilised to select a data sample of more than 9 million collision events. The multiplicity, pseudorapidity, and transverse momentum distributions of charged particles are shown in different regions of kinematics and charged-particle multiplicity, including measurements of final states at high multiplicity. The results are corrected for detector effects and are compared to the predictions of various Monte Carlo event generator models which simulate the full hadronic final state.
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38.
  • Abulaiti, Yiming, et al. (författare)
  • Charged-particle distributions in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC
  • 2016
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 758, s. 67-88
  • Tidskriftsartikel (refereegranskat)abstract
    • Charged-particle distributions are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 mu b(-1), recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on the charged-particle multiplicity are presented. The measurements are performed with charged particles with transverse momentum greater than 500 MeV and absolute pseudorapidity less than 2.5, in events with at least one charged particle satisfying these kinematic requirements. Additional measurements in a reduced phase space with absolute pseudorapidity less than 0.8 are also presented, in order to compare with other experiments. The results are corrected for detector effects, presented as particle-level distributions and are compared to the predictions of various Monte Carlo event generators.
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39.
  • Abulaiti, Yiming, et al. (författare)
  • Combination of searches for WW, WZ, and ZZ resonances in pp collisions at root s=8 TeV with the ATLAS detector
  • 2016
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 755, s. 285-305
  • Tidskriftsartikel (refereegranskat)abstract
    • The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb(-1) of pp collision data at root s = 8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the l nu l'l' (l = mu, e), llq (q) over bar, l nu q (q) over bar and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WZ bosons are compared with predictions of an extended gauge model with a heavy W' boson. In addition, direct searches for a neutral diboson resonance decaying to WW and ZZ in the llq (q) over bar, l nu q (q) over bar, and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WW and ZZ bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall-Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension.
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40.
  • Abulaiti, Yiming, et al. (författare)
  • Constraints on non-Standard Model Higgs boson interactions in an effective Lagrangian using differential cross sections measured in the H ->gamma gamma decay channel at root s=8 TeV with the ATLAS detector
  • 2016
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 753, s. 69-85
  • Tidskriftsartikel (refereegranskat)abstract
    • The strength and tensor structure of the Higgs boson's interactions are investigated using an effective Lagrangian, which introduces additional CP-even and CP-odd interactions that lead to changes in the kinematic properties of the Higgs boson and associated jet spectra with respect to the Standard Model. The parameters of the effective Lagrangian are probed using a fit to five differential cross sections previously measured by the ATLAS experiment in the H ->gamma gamma decay channel with an integrated luminosity of 20.3fb(-1) at root s= 8TeV. Inorder to perform a simultaneous fit to the five distributions, the statistical correlations between them are determined by re-analysing the H ->gamma gamma candidate events in the proton-proton collision data. No significant deviations from the Standard Model predictions are observed and limits on the effective Lagrangian parameters are derived. The statistical correlations are made publicly available to allow for future analysis of theories with non-Standard Model interactions.
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